The present disclosure relates generally to a method and apparatus for analyzing weld strength of friction stir spot welds, and particularly to using eddy currents for analyzing weld strength of friction stir spot welds in an aluminum workpiece.
Friction stir spot welding (FSSW) uses a rotating tool that is driven through a stack of sheets that are to be welded together. This creates a mechanically mixed region in the sheets that holds the stack together. A hole is left when the tool is extracted. One of the key features of FSSW is the penetration of the tool through the stack into the bottom sheet. The target penetration is roughly half way through the bottom sheet. If the penetration is too shallow, the weld strength is reduced. If the penetration is too deep, the outer surface may be distorted or perforated or the tool and anvil may be damaged. To ensure the quality of welds and to prevent damage to the welder, a nondestructive method for measuring the remaining metal thickness and determining the strength of the weld is needed. Accordingly, the art of friction stir spot welding would be advanced with an improved nondestructive method for measuring the remaining metal thickness and determining the strength of the weld.